1. Field of the Invention
This invention relates to a method for treating wastewater, and more particularly, to a method for treating landfill leachate.
2. Brief Description of the Background of the Invention
Landfill leachate is seeped wastewater of complicated chemical composition formed when landfill comes to contact with liquids such as rain water. Landfill leachate generally contains high concentrations of various contaminants, including high BOD compounds, high COD compounds, heavy metals, and ammonia nitrogen compounds, as well as other constituents that are difficult to degrade biologically, such as naphthalenes, phenanthrenes and other aromatic compounds, halogenated aromatic compounds, phosphonolipids, phthalic anhydrides, phenols, anilines, and others. Among these are many compounds exhibiting carcinogenesis, teratogenesis and/or mutagenesis. Landfill leachate has strong repugnant odor.
The treatment of landfill leachate is based mainly on the purification by biological and chemical methods, which include degradation of organic substances via metabolic pathways of microorganisms, and via anaerobic and aerobic processes.
As described, for example in Chinese Patent Application No. CN1478737A, the treatment of landfill leachate can include the steps of removing ammonia nitrogen compounds present in the leachate by electrolysis; degrading the leachate biologically with activated sludge in conjunction with filtration through a hollow fiber membrane (MBR/CMF methods); reverse osmosis; and final purification to meet the various standards for water consumption.
This method of treatment, however, has the significant drawback of inhibition of the leachate-degrading activity of activated sludge by high concentrations of ammonia nitrogen compounds present in the leachate. The drawback is associated with the different conditions that are needed for removing ammonia nitrogen compounds, high COD compounds, and high BOD compounds from leachate by biological degradation.
In order to increase the efficiency of leachate degradation by activated sludge, pre-removal of ammonia nitrogen compounds (NH3—N) is generally required. However, during the pre-removal stages, most ammonia nitrogen compounds tend to be discharged directly into the atmosphere causing secondary pollution. In addition, treatment processes employing Membrane Bioreactor and Continuous Membrane Filtration (MBR/CMF) methods are characterized by high equipment and high operating cost associated with high complexity of these processes and high cost of hollow fiber membranes that are employed. The biological degradation processes are generally inefficient, and expensive.